A two-part study is being undertaken to evaluate a hepatitis B vaccine being produced by NIAID. In the first phase baseline seroepidemiologic data were obtained in 10 dialysis units in New York Blood Center and the Metropolitan Washington Renal Dialysis Unit. When the hepatitis B vaccine became available (approximately Fall 1979) a prospective, controlled, randomized double blind trial of its efficacy was started in these same dialysis units.